The present application claims priority under 35 U.S.C. xc2xa7119 to Japanese Patent Application No. 2000-015355, filed on Jan. 25, 2000, entitled xe2x80x9cCubic boron nitride-based sintered material and manufacture thereofxe2x80x9d.
The contents of this application are incorporated herein by reference by their entirety.
1. Field of the Invention
The present invention relates to a cubic boron nitride-based sintered material efficiently usable at least as tool materials for such as high speed cutting tools for high grade cast iron represented with Ni-Resist cast iron and austempered cast iron and also relates to a method for manufacturing thereof.
2. Discussion of the Background
A Ni-Resist cast iron is a nickel-chromium-copper type austenite cast iron comprising austenite matrix and graphite existing in the matrix and has a chemical composition containing Ni in a range of 13.5-17.5%, Cu in a range of 5.5-7.5%, Cr in a range of 1.0-2.5%, 3.0%or more of C, Si in a range of 1.0-2.8%, and Mn in a range of 0.5-1.5%. Being excellent in wear resistance, heat resistance, and corrosion resistance as compared with a common cast iron, the Ni-Resist cast iron has been widely used as a material for a machine part required to have high temperature strength and hardness in corrosive atmosphere. Especially, the Ni-Resist cast iron has recently been used much mainly as essential and important parts composing an automobile because of further heightened power of an automobile.
In order to process a high grade cast iron represented with this Ni-resist cast iron and an austempered cast iron into a final shape and size of the essential and important parts or the like, cutting process is generally required after casting. A cutting processing tool for the high grade cast iron has to be capable of quickly carrying out processing with a required processing precision without vain. In the case where the edge of a tool is worm or broken owing to chipping, surface roughening and flush occur in the processed surface of the high grade cast iron. Therefore the required size precision and surface roughness cannot be achieved to result in inferior quality and impossibility of output of the cast iron as a product.
Hence, in the case where the tool is worn out or gets defectiveness as mentioned above, the tool has to be replaced immediately. Since the tool replacement leads to productivity decrease, it has to be avoided as much as possible.
Consequently, in order to carry out cutting processing at high efficiency for a high grade cast iron represented with a Ni-Resist cast iron and an austempered cast iron, it has been highly expected to obtain a cutting processing tool which is free of the wear and breaking of the edge thereof by chipping and has a long life.
As a cutting processing tool capable of solving the inconvenience, for example, a ceramic sintered body containing TiC, Al2O3, and a SiC whisker has been proposed as described in Japanese Patent Laid Number 8-16028.
Further, as described in Japanese Patent Laid Number 64-4986, a cubic boron nitride-based sintered material containing either or both of Si3N4 and Al2O3, and Ti2AlN as a binder has been proposed as a cutting and processing tool for a cast iron. Also as described in Japanese Patent Laid Number 64-4987, a cubic boron nitride-based sintered material containing Si3N4, Si2W and Ti2AlN as a binder has been proposed.
Some of the inventors of the present invention have also proposed before, as a cutting processing tool material suitably usable for a high grade cast iron, a cubic boron nitride-based sintered material characterized by sintering a powder of Ti(1-x)AlNx (x varying from 0.05 to 0.70) and a cubic boron nitride powder, and the method for manufacturing the material.
However, the cutting processing tool materials of related arts have the following problems. That is, the ceramic sintered body containing TiC, Al2O3, and a SiC whisker has an advantageous point that it can be manufactured at low cost since no cubic boron nitride is contained, but the ceramic sintered body cannot provide durability which is enough to prolong the life to a desired level.
On the other hand, the cubic boron nitride-based sintered material is supposed to have excellent properties to a general iron cast as compared with the above described ceramic sintered body containing a SiC whisker. However, the conventional cubic boron nitride-based sintered material has not yet provided satisfactory durability to a high grade cast iron.
Further, the cubic boron nitride-based sintered material produced by sintering a powder of Ti(1-x)AlNx (x varying from 0.05 to 0.70) and a cubic boron nitride powder has excellent properties to a spheroidal graphite cast iron, which belongs to the high grade cast iron and is hard to be processed as compared with a general cast iron, but it has not yet provided satisfactory durability to a high grade cast iron represented with a Ni-Resist cast iron and an austempered cast iron.
That is, a high grade cast iron such as a Ni-Resist cast iron and an austempered cast iron is excellent in wear resistance as compared with a spheroidal graphite cast iron and a general cast iron, and the hardness of the structure itself is further heightened during the cutting since the austenitic structure is transformed to a martensitic structure owing to the stress induction by processing stress at the time of cutting. Hence, even in the case where a foregoing conventional cubic boron nitride-based sintered material is used as a cutting tool, the tool does not provide durability which is enough to prolong the life to a desired level.
Consequently, it has been strongly required to develop an economical cutting tool which is capable of cutting a high grade cast iron represented with a Ni-Resist cast iron and an austempered cast iron at a high speed and has a long life.
While the conventional problems is taken into consideration, the present invention is developed to provide a cubic boron nitride-based sintered material with excellent durability usable for a cutting tool material which is capable of cutting at least a high grade cast iron represented with a Ni-Resist cast iron and an austempered cast iron at a high speed and has a long life, and a method for manufacturing such a cubic boron nitride-based sintered material.
According to one aspect of the invention, a method for the production of a cubic boron nitride-based sintered material includes preparing a starting mixture by mixing particles of cubic boron nitride with a binding powders based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7); subjecting the starting mixture to a sintering process under pressure and at the same time at a high temperature; and recovering a sintered product.
According to another aspect of the invention, a method for the production of a cubic boron nitride-based sintered material includes coating particles of cubic boron nitride with a binding powder based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7) to form coated starting particles; subjecting the coated starting particles to a sintering process under pressure and at the same time at a high temperature; and recovering a sintered product.
According to another aspect of the invention, a method for the production of a cubic boron nitride-based sintered material includes coating particles of cubic boron nitride with a first binding powder based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7) to form coated starting particles; preparing a starting mixture by mixing the coated starting particles with a second binding powder based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7); subjecting the starting mixture to a sintering process under pressure and at the same time at a high temperature; and recovering a sintered product.
According to another aspect of the invention, a cubic boron nitride-based sintered material is provided by sintering particles of cubic boron nitride with a binding powder based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7), wherein the sintered material further comprising TiOy that is formed in situ by sintering in the adjacency with the particles of cubic boron nitride, with y varying from 1 to 2, and the binding powder and particles of cubic boron nitride, as composed to be sintered, comprising 30 to 95% of cubic boron nitride and 70 to 10% of the binding powders, with the concentration of each component of the system being within the range of 1 to 25% by percentage to the whole volume combined.
According to the other aspect of the invention, a cubic boron nitride-based sintered material is provided by sintering particles of cubic boron nitride with a binding powder based on the system of TiCN, Si3N4, Al2O3, and CrxN (x varying from 1 to 2.7), wherein the sintered material further comprising TiOy that is formed in situ by sintering in the adjacency with the particles of cubic boron nitride, with y varying from 1 to 2, and the binding powder and particles of cubic boron nitride, as composed to be sintered, comprising 30 to 95% of cubic boron nitride and 70 to 10% of the binding powders, with the concentration of each component of the system being within the range of 1 to 25%, by percentage to the whole volume combined, with SiC admixed thereto in an amount of 1 to 20% relative to the whole volume.